Usurper
by Invader ZaiFae
Summary: When a strange girl sporting mechanical legs interferes in a Titans’ mission, Starfire suspects the worst. There's a better summary inside. Rated mostly for language.
1. Interloper

A Teen Titans/Invader Zim/X-Men: Evolution Crossover 

What started out as a routine bust of a routine burglary attempt for the Titans rapidly diverges from routine when it is interrupted by a girl on slim four mechanical legs, and it has Starfire worried.  Why shouldn't she be—doesn't the most domineering race within galaxies use the exact same utilities?  Robin believes Star, and sends the team out after the girl.  Will they find her?  Who is she?  Or perhaps more pertinent…_what_ is she?

Disclaimer:  I claim absolutely no ownership of anything in this story, with the exception of the mysterious girl.

A.N.:  Hello, all, and welcome to 'Usurper,' my first Teen Titans fic.  Thanks for reading this far, and I hope you'll read on to the end.  I'll try not to keep this too long, but I have a note or two I'd like to make before I start.

First, as I said already, this is my first TT fic, and already it is nearing completion.  So while I accept any and all criticism (except maybe flames), please keep in mind that any changed that are suggested will not come into effect until later chapters, if at all.  Thank you.

Next, as you can see, I've incorporated a character of my own into this story.  While I tried my best not to let her evolve into a Mary Sue, I can't guarantee that she will not have any MS-like moments.  If you can't stand even partial Mary-Sues, please do not read on.  Again, thank you, and you have been warned.

Enjoy.

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It was a quiet day in the Titan's Tower.

Well, okay, it was as quiet as it got during daylight hours.  The sounds of video game effects could be heard echoing throughout the main room of the edifice, but once one got a few floors away from all that, it was silent once again.  Of course, there was only one person down in the silent areas of the tower, as could be considered normal; the other five were gathered in the main room.  It was typical for Raven to be meditating this time of day, just as it was typical for Cyborg and Beast Boy to consistently attempt to one-up one another through the medium of virtual reality.

Starfire and Terra were happily giving each other manicures across the table in the kitchenette while the boys played, and watched each other play, 'Gore Master 3000.'  Starfire had had Terra paint her nails the same color as her vivid red hair, but since the other could not decide what color she wanted hers to be, so they were just doing each nail a different color. 

"Ooh, I like this one!" Terra said brightly, holding her hand up and admiring the turquoise Starfire had just applied.  "It's pretty."

"It reminds me of the color of the hydrogen seas of the moons orbiting Tamaran!" Starfire chirped, swirling the paint around in the bottle thoughtfully.  "Would you like me to do them all that color?"  Terra inspected the nail closer, contemplating it for a moment.

"Well, it would clash with my colors," she mused, "but it's only a little polish, right?  It'll come off in a week anyway!"

"Is that a yes?" Starfire asked, one eyebrow raised quizzically.

"That's a yes!" Terra confirmed with a grin, laying her hand on the towels spread on the table to protect from any spillage.  "Paint me, sister!"

"But I am not related to you…"

"It's an expression, Star," Terra laughed. 

"Oh," Starfire said simply, before grinning and preparing to clean all of the other colors off Terra's hand.  She had only just started, though, when a loud blaring alarm broke through all the noises in the room, alerting everyone to some trouble in the city their tower overlooked.  Robin hopped to his feet, the carefree expression that had been on his face only a moment before already whisked away by a serious one.

"Titans, trouble!" he declared unnecessarily.  "Let's go!"  There was a flurry of smoothly practiced movement as the Titans abandoned the room for the nearest exit, met there by Raven.

It was not a new foe that faced them when they arrived with a flourish outside the hub of the disturbance.  Actually, it was a bit anticlimactic to see Gizmo scaling the outer façade of a dignified looking old jewelry shop, a rather large, full sack clutched to his chest.  The tiny villain wasn't nearly as much of a threat to all five of the Titans when alone, and if the other two Hive graduates had been around, they would have shown themselves by now.  They weren't really a group for stealth, as it were. 

Starfire took to the air at Robin's command, darting in close enough to seize one of the spider-like legs Gizmo was employing and pull back, jerking him free of the building and dropping him to the ground.

"Hey!" he squealed in his little boy's voice.  "What was that for, you stupid booger-face?"

"For doing naughty things," Starfire chided.

"Yeah," Cyborg chimed in.  "And for that, you should get a time out!"  There was a flurry of movement as the big android advanced on the little tech-wizard, who retreated and then leapt over him, still using the spider-legs.  He started to scramble away, but found his path blocked by a sudden wall of rock, summoned and thrown up by Terra.  He used that as a pivot-point, instead, bouncing off and scuttling in a new direction. 

"Nasty slime-brains!" he sneered.  "Get out of my way!"  He didn't see Robin as the nimble teen leapt down on him from above, knocking him to the ground.  Gizmo grunted as he hit and rolled, the spider-legs retracting into the little round pod on his back so they didn't get damaged.  He rolled right to his feet, though, ducking under the swipe Beast Boy, now in tiger form, took at him.  He ran off as fast as his short little legs could carry him, still holding the sack that held, presumably, jewels pilfered from the nearby shop.  Gizmo kicked at Robin's shin as the leader of the Titans reached for him, pushing between the startled lad's legs and bolting across the open street beyond.  Tapping one of the buttons on the control pad in the center of his chest, a small round object dropped into his hand.  He depressed a circle in the top and hurled it towards the Titans.  It exploded into a cloud of billowing, choking smoke that enveloped and, presumably, blinded them.  "See ya later, nerd-buckets!" he crowed, pressing another button on his chest, and in a roar of jets, he was gone.

Had the little cue-ball not been so assured that he would be getting away unopposed, he might have bothered to look behind him and note the dark-clad girl who rose above the cloud, eyes glowing as she exercised her own special abilities and pursued him.  Raven followed from above, watching as he dropped to a convenient rooftop and extended the spider-legs again, probably to save the jet's fuel.  He dropped back down to the ground not soon after that, taking a moment's refuge in an alley before beginning to sneak out.  This was the opportunity she had been waiting for, and Raven prepared to drop on him from above.  She never got the chance.

Gizmo was intercepted by a blur from a corner of the alley, one that tackled him around one of the spider-legs.  It resolved into a girl, short and brown-haired, who grinned widely as she tugged on the end of the leg she had caught.

"Hey, you scum-sucker!  Let go of that!" Gizmo cried, swaying unsteadily on only three of the artificial limbs and trying to pull the other free.  "You'll break it!"  Raven came in a little closer, staying her attack for a moment so she could see how this would play out.

"Nice mechs," the girl said as if she hadn't heard him.  "Well-articulated, though I bet they're unwieldy, being unjointed for so long a stretch like this."  She twisted the leg to one side, apparently examining it.  "Construction looks a little weak, though.  Too badly seamed.  These could be split, easy."

"How would you know?" Gizmo growled, still trying to pull the leg from her hands.  "You mutated freak, there's no way you could have seen anything like these before!  They're one of a kind."  The girl looked up at him, her face twisting for a moment in an expression that looked to Raven like pure anger.  It disappeared quickly, and she grinned wickedly. 

"Wouldn't know, eh?" she asked sweetly.

"Yeah, you spazoid!  Now get offa me!"  She shrugged, looking for a moment as if she were going to do as he requested.  Then she jerked the leg towards her, jumping back a few steps and pulling Gizmo off his precarious balance.  He stumbled towards her, and was completely unprepared when she swung what she held back like a baseball bat and forward again, releasing and sending him flying towards the end of the alley.  She dropped one shoulder, catching the strap of the backpack that fell off of it, and zipped the pack open.  Raven ignored Gizmo for a moment as the girl extracted a bundle of shimmering, silvery cloth from the knapsack.  She unwrapped the bundle, dropping the cloth to the ground in a liquid heap.  She held in her hand then what looked like a metal teardrop, slightly flattened and sliced in half.  It was a metallic off-white color, with three brown spots on it.  She held it up, pointed end cupped in her hand, and reached behind herself, pushing away a thick plait of brown hair and holding the flat side towards her back.  Raven thought she saw two silver cables shoot out towards the girl, and there was no mistaking the look of pain that appeared on her face.  The thing was flush to her T-shirt when she took the hand away.

Gizmo had recovered by then, and gingerly picked his way back to his feet.  As soon as he was stable, he glared down at the girl, apparently thinking up another convoluted insult to throw at her.  He didn't say a word, though, before the bit of metal on her back shifted and opened up, sprouting four long mechanical legs that lifted her high above him.  They were longer than his, and made of a lighter colored metal.  They seemed impossibly thin, as if they wouldn't be able to support her weight.  The balls in the joints of the limbs were the same brown as the spots, and the tips of them incredibly thin- and dangerous looking. 

"What was that about not knowing?" she asked with a smirk, folding her arms over her chest.    Gizmo's eyes were wide with surprise, and he took a step back, before turning and leaping onto the nearest wall.  The girl took a few steps after him, and at first, the motion of her legs seemed less under control than his.  However, when she took to the walls, she seemed to dance up them, unafraid to jut herself several feet out from the surface.  Gizmo held himself as close to the wall as possible, as if he were afraid he were going to fall at any time, and scuttled like an insect.  She reached the roof of the building before he did, and was waiting for him when he emerged over the ledge.  Raven drifted higher into the air, still watching quizzically.  

"I'm disappointed," the girl said frankly, shaking her head.  "Not as nimble as I would have—"

The girl was cut off by the sight of a monolith of rock rising into the air behind Gizmo, carrying Terra, Cyborg, and Robin.  Beast Boy, in falcon form, and Starfire rose above it, and Raven joined them.  The mech-legged girl's face blanched, her mouth falling open slightly.  Gizmo, oblivious to the Titans behind him, laughed triumphantly. 

"Something wrong, dirt-for-brains?" he asked.  She didn't respond, leaping forwards and seizing the nearest of his legs, hauling him around once again and launching him towards the rock.  The Titans scrambled to get out of the way, and Raven pivoted and dove after the screaming little techie, who was heading at a higher-than-normal speed towards the asphalt below.  The girl took the opportunity and leapt off the top of the building, vaulting to the next one and skittering over the roof at high velocity, mechanical legs blurring, they were going so fast.  Robin jumped lithely from Terra's rock, after Gizmo.  Beast Boy and Terra followed with Cyborg, but Starfire, glancing down at her other teammates, made a quick decision and followed the girl.  She craned her head over her shoulder, saw Starfire, and increased her speed.

"Wait!" Starfire called.  "Why are you fleeing?  Slow down!"  The lass disappeared abruptly from view and Starfire feared for a moment that she had fallen, but when she flew over the narrow canyon between the two buildings, she saw that the girl had straddled the crack with her mech legs and was picking her way down.  She looked up, and Starfire was hurt to see that she looked afraid.  She fell the last dozen feet to the ground and, retracting her mechs, took off on foot.  "Wait!" Starfire called again, futilely, as she pursued her, staying above the heads of the pedestrians the girl pushed to either side as she ran.  Starfire knew that humans were not well known for their stamina, and was content to simply tail this one until her exhaustion forced her to a stop.  As she flew above the heads of the bewildered city citizens, she scrutinized the girl, looking for what she had thought she had seen up on the roof.  It was not hard to see, the teardrop shaped hump of metal on the girl's back.  That was—

The little one swerved suddenly, ducking into the mouth of a narrow alley.  Star dropped to her feet, taken by surprise, and peered around the corner.  She found herself staring down the barrel of a gun.  At least, she though it was a gun; stepping back hastily, she recognized the smooth contours and technicolors of a laser blaster— 

"Leave me alone."

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So that's it for this chapter.  All reviews are appreciated, and they will help make updates come quicker.  Thanks for reading!


	2. While We're Dancing All Alone

I have a lot of this story written already, so here's an update!

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"And then she shoved past me, and ran into a department store, and she was gone," Starfire said, shrugging.  "I looked inside, but I could not see her.  There were too many people."

"Interesting, Star," Robin commented, tapping his fingers against the tabletop in the kitchenette in the Tower.  Terra was lounging nearby, gnawing on the end of a pretzel stick.  The other Titans had gone their own ways on returning from their clash with Gizmo, and Starfire didn't know where they were.  "That's interesting.  What made you follow this girl, again?"

"I…I thought I recognized her," she admitted slowly.

"Recognized her?"

"Well, not her specifically," she clarified quickly.  "I recognized her mechanical limbs."

"Yeah, they were like Gizmo's," Terra interjected, slurring her words slightly through her mouthful of pretzel.  Starfire shook her head quickly, her hair falling into her eyes for a moment, until she pushed it out of the way.

"No, they were not," the Tamaranean said breathlessly.  "They were Irken.  That was an Irken PAK on her back."

"Irken," Robin repeated blankly.

"What's an Irk-en?" Terra asked, sounding out the word carefully. 

"They are a race of creatures," Starfire said, eyes wide.  "We compare them to _telluchians_ on my planet, but I suppose you could say that they resemble insects on this one, with big eyes and antennae and green skin.  They are trying to conquer the universe; their Empire is already extensive."

"And this…do you think this girl was an…Irken?" Robin asked, leaning forward.  Starfire shrugged.

"I do not see how she could not have been," she said.  "The Irken race jealously guards everything of theirs, including their technology.  As far as I know, she has to have been Irken."

"But why would one of these things be on Earth?"

"The only times Irkens move off their conquered territories," Starfire said, apparently struggling to remember, "is if they're part of a diplomatic envoy to an ally planet, or scouting it out for conquering."  A look of stunned realization crossed her face.  "She could be an Invader!" she gasped. 

"And that's not good, right?" Robin asked.  She nodded quickly.

"Well, what can we do about it?" Terra asked, setting her pretzel rod aside. 

"Track her down?" Starfire suggested.  "I would not know.  Our people repelled an attempted Irken invasion millennia ago, long before I was born.  The exact methods are a little unclear now."

"Tracking her down to question her couldn't hurt," Robin mused, tracing a pattern in the design on the tabletop with an idle finger.  "Even if she's not one of these…Irkens…"

Starfire nodded enthusiastically.  "We could do so now!"

"The sooner we start, the better chance we have of finding her, actually," Robin said, pushing his chair back from the table and standing up.  He leveled a gaze at the two teens.  "Will you girls round up the others?  We should get out there before this mystery being gets a chance to get too far from where you saw her last."

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Of course, finding one non-descript and possibly alien girl in a city of several thousand equally non-descript people was a lot harder to say than to do.  They started at the department store Starfire had reported her disappearing into and worked their way out from there.  Beast Boy had volunteered to canvass the big park in the center of the city on the off chance that she had hidden herself in plain view, but he had a slightly ulterior motive.  He didn't really expect this girl they were looking for to be there, but he did expect a lot of other cute chicks to, and well, who could blame him if he got a little sidetracked, yes?

There was a particular spot along the main path winding its way through the park that often attracted crowds because of the street performers who gathered there.  The cobbled lane was wide and flat, and the copses of trees were a distance to either side of it—it offered a lot of space without the park-goers having to venture off the path if they didn't want to.  Beast Boy trekked up to the top of a small rise and looked down on the people below.  There was that guy with the weird accent who did the card tricks in his usual spot.  Beast Boy had seen him there often recently—the man drew a regular crowd with his demonstrations of sleight-of-hand now that the word of him had spread around.  He had competition today, though; there was girl with a boom box and a little pleather-and-satin getup across the way.  While he made the female portion of the park-walkers ooh and aah over his subtle flirting and impressive magic, she was entrancing the males with her swaying, coquettish dancing.

Beast Boy watched them both, scanning the crowds regularly for any sign of anyone who fit the description that both Starfire and Raven had seen.  He didn't see anyone with a metal teardrop on their backs, though, and that was really what he was looking for.  There were a lot of girls with braided brown hair—heck, even the dancer had her deep brown hair held in a braid, though it was coiled up in a bun at the back of her head, with two long, thin sticks stuck through it for a more authentic Japanese look.  The outfit she was wearing looked Japanese, he realized, and the song playing definitely sounded so.  The lyrics were pretty cool too.

Slowly, the number of people trickled away so that there were only the two performers left in the park.  The man stuck his hands in the pockets of his trenchcoat and, as Beast Boy watched, approached the girl.  She had been folding up the odd silvery cloth she had been standing on but looked up now—up and up.  He was much taller than she.  Beast Boy got to his feet, taking a few steps down the embankment.  The man didn't look happy.

"What y' doin', _cherie?_" he asked brusquely, crossing his arms and looking down at her, his eyes shadowed behind sunglasses like they always were.  "Y' tryin' t' drive Remy insane, dancin' like dat?"  The dancer held her hands up, the cloth flowing from one, falling out of the folds she had tried to put it in.

"I'm sorry, man," she said quickly, ducking her head submissively.  "I didn't mean to…uh…distract you or whatever it was I was doing.  I was just trying to make a couple of bucks."

"Y' be comin' back tomorrow?" he asked, sounding like he was trying to be threatening.  Beast Boy thought he sounded a little hopeful.  She shook her head.

"No way," she said vehemently, before a grin spread over her face.  "Gambit."  The man's jaw dropped, and he looked shocked. 

"Mythos," he said slowly, moving his sunglasses down the bridge of his nose to get a better look at her.  "De boss been lookin' for you."

"Your boss is a manipulative, megalomaniac psychopath with no chance whatsoever of achieving his goals," she said matter-of-factly, before ducking and, in one smooth motion, picking up the boom box and (after slipping the CD discretely into her hand) throwing it at the man.  He reacted quickly enough to catch it before it hit him, but she took his moment of distraction to stuff the cloth into the pack at her feet and run.  She bolted in the direction of Beast Boy, plunging past him and over the grassy knoll and into the trees beyond.  The man with the accent pursued her to the top of the hill, but stopped there.  He'd lost her in the trees, and he knew it. 

"_Merde __alors,_" he muttered, turning to glance at Beast Boy for a moment, before stalking nonchalantly back down the hill.  Beast Boy remained at the top of the hill for a moment, before making his own way down.  Now that all the people had gone, he figured he'd better start searching some of the other parts of the park for the girl he was supposed to be looking for.  He wound his way out of the open space and into an arm of the thick stand of trees the girl had disappeared into, looking around and winking at a pair of chicks strolling towards him.  They giggled, and kept going.  Suddenly, another person appeared on the path, but this one didn't come into view around the bend ahead like the others.  She broke onto it from the woods on his right.  It was the dancer.

She sat down in the thin strip of grass bordering the path, and opened up her pack.  She extracted that strange, silvery cloth, and began packing it back in, arranging it carefully within.  It looked to Beast Boy like she was wrapping it around something, but he couldn't see what. 

"Hey, are you all right?" he asked as he approached.  The girl looked up wildly, eyes wide open.  The pack spilled from her hands, thudding heavily into the grass as she hopped to her feet.  She relaxed an instant later, though that wary look never left her eyes.

"I'm fine," she said slowly, eyeing him.  "Why?"

"Well, I saw that guy hassling you in the park…" Beast Boy trailed off, uncertain if he sounded stupid or not.

"Oh," she said simply.  "Uh…thanks.  I'm fine, though, no worries about that."  Beast Boy nodded, looking away. 

"Just figured I'd ask," he said with a little chuckle.  He bent down, grabbing the strap of her pack and not seeing the panicked light that came into her eyes as he did so.  He lifted it, grunting slightly at the unexpectedly heavy weight of it.  He put one hand underneath so it didn't fall, and felt, albeit through several layers of cloth, an expanse of smoothness.

Like metal.

Rounded metal.  Almost as if it were in the shape of a teardrop.  His eyes locked with hers for a moment, but she looked away quickly, snatching the pack back from him and getting hastily to her feet.

"Er, thanks," she said quickly, backing a step away.  A shout from behind him startled them both.

"Hey BB!  Any luck?!" Beast Boy turned to see Cyborg waving at him, followed by Raven.  He turned back to the girl, but she had already bolted.  He pointed.

"Her!" he yelled, before giving chase.  He heard Cyborg's steps hitting the cobbles loudly as he broke into a run, quickly catching up to the shorter-legged Beast Boy.

"Her?"

"Her!"

Raven flew over them both, eyes glowing white in the shadow under her hood.  Beast Boy could see her lips moving and faintly heard her ritual 'Azarath Metrion Zinthos!'  A wave of dark telekinetic energy swept from her outstretched arms, shaped vaguely like a hand held wide, and closed on the girl, lifting her, struggling, into the air.  She kicked, but it was useless against something that wasn't there.  Raven lifted one hand, drawing the girl closer, and waited for Beast Boy and Cyborg to catch up.

"Cyborg?" she asked, her voice toneless as usual.  The big Titan nodded, activating his communicator.

"Robin," he called into it.  "Starfire.  Terra.  We found the girl. Meet us back at the tower.  Over."  He waited for all three affirmative replies before turning it off again.

"Totally sweet catch, Raven!" Beast Boy said with a grin.  Raven inclined her head to acknowledge the compliment, but didn't reply, or even look his way.  Beast Boy hadn't expected her to, though—her concentration was still on the girl, who had stopped her kicking and was now glaring murderously down at them.

"Come on," Cyborg said, striding over to the fallen pack and stereo and stopping to pick them up.  "Let's get back to the Tower."

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So thank you to my reviewer!  I updated, Sam!  .

Review, please!


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